Semiconductor fabricating apparatus with function of determining etching processing state

ABSTRACT

When a semiconductor wafer placed in a chamber and having films thereon is etched using plasma generated in the chamber, a change in the amount of lights with at least two wavelengths, obtained from the wafer surface during the processing, is detected. The time between the time at which the amount of a light with one of two wavelengths is maximized and the time at which the amount of a light with the other wavelength is minimized is compared with a predetermined value to determine the state of etching processing.

CROSS-REFERENCE TO RELATED APPLICATION

[0001] The present invention is related to U.S. patent application Ser.No. 09/946,504 filed on Sep. 6, 2001 and U.S. patent application Ser.No. 10/230,309 filed on Aug. 29, 2002.

BACKGROUND OF THE INVENTION

[0002] The present invention relates to an apparatus that fabricatessemiconductor devices through etching processing and more particularlyto a semiconductor fabricating apparatus that has a function ofdetermining the etching processing state such as an etched depth.

[0003] Dry-etching has been widely used in the semiconductor deviceformation process to remove layers of various materials, such asdielectric materials and insulating materials, formed on the surface ofa semiconductor wafer or to form patterns on those layers. In thedry-etching process, it is important to adjust etching during theprocessing of the layers so that an etched depth desired for a layer maybe obtained or so that a thin film desired for a layer may be obtained.Therefore, it is required to accurately detect the end points of etchingprocess and the film thickness.

[0004] When dry-etching a semiconductor wafer using plasma, it is knownthat the light emission intensity of a specific-wavelength lightincluded in a plasma light changes with the progress of the etchingprocess of a specific layer. One of known technologies for checking theetching states, such as the end point of etching process and the filmthickness on a semiconductor wafer, takes advantage of thischaracteristics to detect a change in the light emission intensity of aspecific-wavelength light included in the plasma light during thedry-etching process and, based on this checking result, detects the endpoint of etching process on a specific layer and the film thickness ofthe layer. To increase detection precision, a misdetection caused by afluctuation in the detected waveform generated by noises should bereduced.

[0005] Recently, as the wiring pitch of a semiconductor becomes finerand its density becomes higher, the open area ratio (non-etched area ona semiconductor wafer) becomes lower. This decreases the light emissionintensity of a specific-wavelength light sent from the light sensor tothe light detector. As a result, the level of the sampling signal fromthe light detector becomes lower, making it difficult for the end pointdetermination unit to correctly detect the end point of etching processbased on the sampling signal from the light detector.

[0006] When stopping processing upon detection of the end point ofetching process, it is important that the thickness of the remainingdielectric layer should be equal to a predetermined value. In theconventional process, the time thickness control method is used tomonitor the whole process on the assumption that the etching speed ofeach layer is constant. An etching speed is obtained, for example, byprocessing a sample wafer in advance. In this method, the etchingprocess stops at the same time the elapsed time measured by the timemonitor method becomes equal to the time corresponding to apredetermined film thickness (remaining film thickness in etchingprocess).

[0007] However, it is known that the thickness of an actual film, forexample, an SiO₂ layer formed by the LPCVD (Low Pressure Chemical VaporDeposition) method, varies from time to time. An allowable thicknesserror caused by a process fluctuation during LPCVD corresponds to about10% of the initial thickness of the SiO₂ layer. This means that theactual final thickness of the remaining SiO₂ layer on the siliconsubstrate cannot be measured accurately by the time monitor method. Theactual thickness of the remaining layer is measured finally by thestandard emission spectroscopy. If excess etching is found, the wafer isrejected and discarded.

[0008] A technology for detecting the end point of etching process on asemiconductor wafer by measuring the surface of a wafer with the use ofan interferometer is known. This technology is disclosed, for example,in JP-A-5-179467 (document 1), U.S. Pat. No. 5,658,418 (document 2),JP-A-2000-97648 (document 3), and JP-A-2000-106356 (document 4).

[0009] JP-A-5-179467 (document 1) discloses a method for detecting theend point of etching process by detecting an interference light (plasmalight) using three color filters (red, green, blue). U.S. Pat. No.5,658,418 (document 2) discloses a method for counting the extremevalues (maximum and minimum of waveform: zero-pass point of differentialwaveform) of an interference waveform using a change in the interferencewaveform of two wavelengths with respect to time and its differentialwaveform. The etching speed is calculated by measuring the time requireduntil the count reaches a predetermined value, the remaining etchingtime required until a predetermined film thickness is attained iscalculated based on the calculated etching speed, and, based on thecalculated time, the etching process is stopped.

[0010] JP-A-2000-97648 (document 3) discloses a method that obtains adifference waveform (that uses a wavelength as a parameter) between alight intensity pattern (that uses a wavelength as a parameter) of aninterference light before processing and a light intensity pattern ofthe interference light after or during processing and compares theobtained waveform with the difference waveform read from the databasefor measuring a difference in level (film thickness). JP-A-2000-106356(document 4), which relates to a rotary coating apparatus, discloses amethod for finding the film thickness by measuring a change in theinterference light of multiple wavelengths with respect to time.

[0011] When stopping processing upon detection of the end point ofetching process, it is important that the thickness of the remainingfilm layer is close to a predetermined value as much as possible. Theconventional technology monitors the film thickness by adjusting thetime on the assumption that the etching speed of each layer is constant.The reference etching speed value is obtained, for example, byprocessing a sample wafer in advance. According to this technology, theetching process stops when the time corresponding to the predeterminedfilm thickness elapses.

SUMMARY OF THE INVENTION

[0012] However, when semiconductor wafers with the film structure ofseveral different types are processed in small amounts at a time forfabricating semiconductors, a database for a multiple-wavelengthinterference pattern of differential coefficients must be created, onefor the wafer to be processed and to be fabricating into products.Therefore, when etching processing is performed on a trial basis using awafer with the same film structure as that of an actual wafer, the testcost becomes too high for small-amount fabrication because the wafer isexpensive and as many extra wafers as the number of tests are required.This results in an increased device fabrication cost.

[0013] In the prior art described above, a sample wafer is required alsowhen the film thickness of a wafer to be used is detected for use insetting up the operating conditions of a semiconductor fabricatingapparatus when the thickness detection result is used to process a waferfor fabricating a product therefrom. For example, a wafer is selectedfrom one lot for measuring. This requires a measuring time and a wafer,decreasing the throughput of semiconductor fabrication.

[0014] It is an object of the present invention to provide asemiconductor fabricating apparatus that solves the problems with theprior art described above.

[0015] It is another object of the present invention to provide asemiconductor fabricating apparatus that increases processingthroughput.

[0016] There is described a semiconductor fabricating apparatus etchinga semiconductor wafer, placed in a chamber and having films thereon,using plasma generated in the chamber. The semiconductor fabricatingapparatus comprises a detector that detects a change in an amount oflight with at least two wavelengths obtained from a surface of the waferfor a predetermined time during the processing; and a determinationfunction that compares an interval between a time at which an amount oflight with one of the two wavelengths is maximized and a time at whichan amount of light with the other wavelength is minimized with apredetermined value to determine a state of the etching.

[0017] There is described a semiconductor fabricating apparatuscomprising a detector that, when a semiconductor wafer placed in achamber is etched using plasma generated in the chamber, detects a lightinterference from a surface of the wafer for a predetermined time duringthe etching processing; and a control unit that compares an intervalbetween a time at which an amount of light with one of at least twowavelengths output from the detector is maximized and a time at which anamount of light with the other wavelength is minimized with apredetermined value to control the etching processing.

[0018] In addition, there is described that a thickness of the filmbeing etched is determined if the interval is determined to be smallerthan the predetermined value.

[0019] In addition, there is described that the etching processing isstopped if the interval is determined to be smaller than thepredetermined value.

[0020] There is described a semiconductor fabricating apparatus etchinga semiconductor wafer, placed in a chamber and having a multiple-layerfilm composed of a first film formed a surface thereof and a second filmformed on the first film, using plasma generated in the chamber. Thesemiconductor fabricating apparatus comprises a light detector thatdetects a change in an amount of light with a plurality of wavelengthsobtained from a surface of the wafer for a predetermined time duringwhich the second film is etched; and a detection function that detects athickness of the first film based on a specific waveform obtained froman output of the detector.

[0021] There is described a semiconductor fabricating apparatus etchinga semiconductor wafer, placed in a chamber and having a multiple-layerfilm composed of an oxide film formed a surface thereof and a filmformed on the oxide film, using plasma generated in the chamber. Thesemiconductor fabricating apparatus comprises a light detector thatdetects an amount of light with a plurality of wavelengths obtained froma surface of the wafer for a predetermined time during which the filmformed on the oxide film is etched; and a detection function thatdetects a thickness of the oxide film based on a specific waveformobtained from an output of the detector.

[0022] There is described that, when a change in an amount ofinterference light from the surface of the wafer with respect to time isdetected for the plurality of wavelengths, a characteristic change in anoutput of the light detector is detected.

[0023] To detect the maximum value and the minimum value from a lightfrom a wafer, a theoretical interference analysis is made in advanceusing the optical physical characteristic values of a material to beetched to obtain a change in the interference waveform for eachwavelength. Then, for a predetermined film thickness, the two differentwavelengths whose interference waveforms have the peak-troughcorrelation are selected. In addition, the interference waveforms of thetwo wavelengths are measured and, through differentiation, thezero-cross times of the differential values are found. If the zero-crosstimes are within a predetermined value, it may be determined that adesired film thickness is attained.

[0024] A differential interference pattern may be created for aninterference light with multiple wavelengths that are obtained duringthe etching processing to attain a desired film thickness. With thismultiple-wavelength differential interference pattern stored each time awafer is etched, the data values of the interference patterns may beaveraged to give more reliable multi-wavelength differentialinterference data. By using this data to select two interferencewaveforms with different wavelengths, which satisfy the peak-troughcorrelation for the predetermined film thickness described above, theetching condition such as the film thickness may be detected anddetermined more accurately.

[0025] Other objects, features and advantages of the invention willbecome apparent from the following description of the embodiments of theinvention taken in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

[0026]FIG. 1 is a diagram showing the general configuration of asemiconductor wafer etching apparatus with a film thickness measuringapparatus in one embodiment of the present invention.

[0027]FIG. 2 is a diagram showing an example of the vertical section ofa member to be processed 40 for which gate etching is performed.

[0028]FIG. 3 is a diagram showing an example of a change in aninterference light with respect to time for multiple wavelengths duringthe etching processing is FIG. 2.

[0029]FIG. 4 is a flowchart showing a procedure for finding the filmthickness of a member to be processed when etching processing isperformed by the film thickness measuring apparatus in FIG. 1.

[0030]FIGS. 5A-5D are diagrams showing the undercoating oxide filmdependence of a poly-silicon film thickness and the undercoating oxidefilm dependence of a wavelength when etching processing is performed bythe film thickness measuring apparatus in FIG. 1.

[0031]FIG. 6 is a diagram showing a multiple-wavelength differentialinterference pattern and the wavelength dependence of a differentialvalue in a poly-silicon film thickness in another embodiment of thepresent invention.

[0032]FIGS. 7A and 7B are diagrams showing a multiple-wavelengthdifferential interference pattern and the wavelength dependence of adifferential value in a poly-silicon film thickness in the otherembodiment of the present invention.

[0033]FIG. 8 is a flowchart showing the operation of the otherembodiment of the present invention.

DETAILED DESCRIPTION OF THE EMBODIMENTS

[0034] Some embodiments of the present invention will be described withreference to the attached drawings.

[0035] In the description of the embodiments below, the same referencenumerals as those in a first embodiment are used to denote the samecomponents with the similar functionality, and their detaileddescriptions are omitted. In the embodiments below, there is described asemiconductor fabricating apparatus according to the present inventionand a method for measuring etching conditions such as the etching amount(etched depth or etched film thickness) during etching processing of awafer that is a member to be processed. In the description below, “filmthickness” refers to a remaining film thickness in the etchingprocessing.

[0036] A first embodiment of the present invention will be describedwith reference to FIGS. 1-3. FIG. 1 is a diagram showing, with the useof its vertical section and the blocks, the general configuration of thefirst embodiment of a semiconductor fabricating apparatus of the presentinvention. FIG. 2 is a diagram schematically showing the configurationof a wafer to be processed and the overview of light interference in thefirst embodiment. FIG. 3 is a graph showing an example of data obtainedthrough light interference in the first embodiment.

[0037] First, the general configuration of a semiconductor wafer etchingapparatus with a film thickness measuring apparatus according to thepresent invention will be described.

[0038] An etching apparatus 1 has a vacuum chamber 2 containing etchinggas that is decomposed by microwave power into plasma 3. This plasma 3is used for etching a member to be processed 4 such as a semiconductorwafer on a wafer table 5. A multiple-wavelength light, emitted from ameasuring light source (for example, a halogen light source) of a filmthickness measuring apparatus 10, is guided into the vacuum chamber 2through an optical fiber 8 and is focused onto the member to beprocessed 4 at a right incident angle. The member to be processed 4 hasa poly-silicon layer. The emitted light is formed into an interferencelight by combining the light refracted on the surface of thepoly-silicon layer with the light refracted on the boundary between thepoly-silicon layer and the undercoating layer. The interference light isguided through the optical fiber 8 into a spectroscope 11 of the filmthickness measuring apparatus 10 for use in measuring the film thicknessor in determining the end point based on the state.

[0039] The film thickness measuring apparatus 10 comprises aspectroscope 11, a first digital filter circuit 12, a differentiator 13,a second digital filter circuit 14, a differential waveform database(differential zero-cross time accumulator) 15, a differential waveformcomparator (differential zero-cross time comparator) 16, a processingstate determination unit 26, and a result display 17. FIG. 1 shows thefunctional configuration of the film thickness measuring apparatus 10.Actually, the film thickness measuring apparatus 10 may comprise a CPU;storage units such as a ROM containing a film thickness measuringprocessing program and various types of data such as an interferencelight differential waveform pattern database, a RAM containingmeasurement data, and an external storage device; data input/outputdevices; and a communication controller.

[0040] When a member to be processed such as a semiconductor wafer isplasma-etched, the semiconductor fabricating apparatus according to thepresent invention calculates in advance the light interference waveformusing the optical physical property values of the member to be processedand selects in advance the wavelength groups whose differential value ofthe interference light for a predetermined film thickness crosses thezero-value (or takes an extreme value). Data on the positive-to-negativezero-cross (or maximum value) wavelength group λ1 and thenegative-to-positive zero-cross (or minimum value) wavelength group λ2is stored or recorded in a storage unit or a recording unit provided in,or configured for communication with, the semiconductor fabricatingapparatus main body. When the member to be processed 4 is actuallyprocessed, the intensity of the interference light of waveform groups λ1and λ2 is measured to detect the time at which the differential value ofeach wavelength group for the measured interference light intensitycrosses the zero-value (takes an extreme value). Then, the zero-crosstime is compared with a predetermined value to find the film thicknessof the member to be processed.

[0041] The light emission intensity of an interference light with awavelength included in the wavelength group λ1, obtained by thespectroscope 11, becomes a current detection signal corresponding to thelight emission intensity. This signal is then converted to a voltagesignal. A plurality of specific-wavelength signals output by thespectroscope 11 as sampling signals are stored in a storage unit, suchas a RAM, as time series data yij. This time series data yij is thensmoothed by the first digital filter circuit 12 and is stored in astorage unit, such as a RAM, as smoothed time series data Yij. Based onthis smoothed time series data Yij, the differentiator 13 calculatestime series data dij of a differential coefficient value (firstdifferential value or second differential value), which is then storedin a storage unit such as a RAM. The time series data dij of thedifferential coefficient value is smoothed by the second digital filtercircuit 14 and is stored in a storage unit, such as a RAM, as smootheddifferential coefficient time series data Dij. A real pattern of thedifferential values of each wavelength of the interference lightintensity is obtained from this smoothed differential coefficient timeseries data Dij.

[0042] On the other hand, the light emission intensity of aninterference light with a wavelength included in the wavelength groupλ2, obtained by the spectroscope 11, becomes a current detection signalcorresponding to the light emission intensity. This signal is thenconverted to a voltage signal. A plurality of specific-wavelengthsignals output by the spectroscope 11 as the sampling signals are storedin a storage unit, such as a RAM, as time series data y′ij. This timeseries data y′ij is then smoothed by a first digital filter circuit 22and is stored in a storage unit, such as a RAM, as smoothed time seriesdata Y′ij. Based on this smoothed time series data Y′ij, adifferentiator 23 calculates time series data d′ij of a differentialcoefficient value (first differential value or second differentialvalue), which is then stored in a storage unit such as a RAM. The timeseries data d′ij of the differential coefficient value is smoothed by asecond digital filter circuit 24 and is stored in a storage unit, suchas a RAM, as smoothed differential coefficient time series data D′ij. Areal pattern of the differential values of each wavelength of theinterference light intensity is obtained from this smoothed differentialcoefficient time series data D′ij.

[0043] Differential data storage units 15 and 25 store the interferencelight intensity data on the wavelengths, which vary with the filmthickness, or the values of waveforms of the differential data and theirtimes. In particular, the maximum values and minimum values,corresponding to the peaks and troughs of differential data, and theirtimes Tm and T′n are stored. The length of the time between Tm and T′nis compared with a predetermined value pre-set or stored/recorded in thecomparison operation unit 16. If the length of the time between Tm andT′n is smaller than the predetermined value, it is determined that theremaining film thickness has reached or almost reached a predeterminedsize and the remaining film thickness of the member to be processed isdetermined. The result is displayed on the result display 17.

[0044] The inventor and the colleagues have found the following. When afilm formed on a semiconductor wafer is etched, a group of a pluralityof wavelengths, where one of differential waveform data is the maximumvalue and the other is the minimum value, may be selected in theneighborhood of the time at which a specific film thickness is attained.The length of the time between the time when a waveform with awavelength belonging to the groups becomes the maximum or the minimumgets shorter as the film thickness becomes smaller. This means that, fora specific film thickness, the interval between the time when one of thewaveforms becomes the maximum and the time when the other becomes theminimum before or after the maximum time is fixed. With this intervalpre-set as the base, whether or not the specific film thickness isattained may be determined.

[0045] The differential data storage unit 15 stores the change in thedifferential waveform data of the interference light from the wafer 4that is the member to be processed as well as the times at which thevalue of differential waveform data becomes the extreme value (maximum,minimum). That is, data on the times of the peak and the trough of theinterference light intensity that varies with the film thickness isstored. In addition, for a specific range of wavelengths at etchingprocessing time, the differential data value of interference light dataat a predetermined time during processing is sent from this differentialdata storage unit 15 to the display 17 and is displayed on the display17. The data on the times at which the differential value of theinterference light with multiple wavelengths becomes the maximum and theminimum may also be displayed on the display 17.

[0046] The differential waveform comparator 16 compares the time Tm andthe time T′n to obtain the film thickness of the member to be processed.The result is displayed by the result display 17.

[0047] Although only one spectroscope 11 is shown in this embodiment, aplurality of spectroscopes 11 may be used to measure and control a widerange of the area of a member to be processed.

[0048]FIG. 2 shows an example of the vertical section of the member tobe processed 4, such as a semiconductor wafer, to be used in gateetching processing. Referring to FIG. 2, a material to be processed(poly-silicon) 40, which is the film to be processed, is formed on anoxide film 42 that is the undercoating material provided on the wafer(substrate) 4. In addition, a masking material 41 is laminated on thematerial to be processed 40. For example, when etching a gate film, theundercoating material of the material to be processed 40 is an SiO₂insulation film, and a poly-silicon gate layer is formed on apoly-crystal undercoating material corresponding to the source and thedrain. To ensure the independent operation of a gate electrode section48 of each device, a device separation trench 49 is formed by an oxidefilm. In this embodiment, the gate electrode section 48 is provided inthe side in which a Shallow Trench Isolation (STI) 42 is provided belowa mask 71.

[0049] A multiple-wavelength light emitted from the spectroscope 11 orthe plasma 3 is focused, at an almost right incident angle, on themember to be processed 4 including the laminated structure of thematerial to be processed 40 and the oxide film 42 that is theundercoating material. The emitted light guided into the gate electrodesection 48 where the undercoating material 42 is thin is formed into aninterference light 95A composed of the light reflected on the surface ofthe material to be etched 40 and the light reflected on the boundarybetween the material to be processed 40 and the undercoating material42. Similarly, the emitted light guided into the device separationtrench 49 where the undercoating material 42 is thick is formed into aninterference light 95B composed of the light reflected on the surface ofthe material to be processed 40 and the light reflected on the boundarybetween the material to be processed 40 and the undercoating material42. The interference intensity of these interference lights is reducedas the undercoating oxide film becomes thinner. Therefore, theinterference lights 95A and 95B are in the relation 95B>95A.

[0050] The reflected light is guided into the spectroscope 11 togenerate a signal whose intensity varies according to the thickness ofthe layer of the material to be etched 40 that is being etched. Amongthe interference lights detected by the spectroscope 11, theinterference light 95B from the thicker processing film part is dominantover the interference light 95A. In this embodiment, the etching state,such as the film thickness and the etching trench depth detected by theinterference light, may be obtained more accurately from theinterference light reflected on the material above the device separationtrench 42 (for example, film thickness 46).

[0051] The display 17 is a liquid crystal display or a CRT display, anotification unit that notifies that a predetermined film thickness oran end point is reached with the use of light or sound, or a combinationof them. In this embodiment, the display 17 having a display capable ofdisplaying the measurement data as a graph and a unit notifying thestate with the use of light and sound is provided.

[0052] In addition, the apparatus in this embodiment has a functionthat, with the use of measurement data displayed on the display 17,displays specific information desired by the user who views thedisplayed data or allows the user to specify information necessary todetect specific information or to perform calculation. Included in thisfunction are the specification function, such as a pointer allowing theuser to specify a specific or any point on the time-wavelengthcoordinate displayed on the display 17 or the data at that point; thefunction used to detect data values at a specified point or to calculatespecific amounts, such as the time between specific times or awavelength and amounts indicating the etching state such as an etchingspeed and a film thickness; and the function to display those amounts inan easy-to-identify position.

[0053] The unit calculating the amounts described above may be acalculator in the apparatus or a separate calculator located remotelyfrom the apparatus and capable of sending and receiving measured ordetected data via the communication unit.

[0054]FIG. 1 shows the functional configuration of the apparatus formeasuring an etching amount. Actually, the measuring apparatus 10,except the display 17 and the spectroscope 11, may comprise a CPU;storage units such as a ROM containing an etching depth and filmthickness measuring processing program and various types of data such asan interference light differential waveform pattern database, a RAMcontaining measurement data, and an external storage device; datainput/output devices; and a communication controller. This applies alsoto the other embodiment described below.

[0055]FIG. 3 is a graph showing a change in multiple wavelengths withrespect to time for data generated by differentiating interference lightdata detected by the semiconductor fabricating apparatus in thisembodiment. As shown in this figure, from several waveforms each with awavelength, a pair of waveforms may be selected wherein, in theneighborhood of the time at which one of the waveform reaches theextreme value (maximum), the other reaches the minimum. The inventor andthe colleagues have found that the difference between the time at whicha waveform with one wavelength reaches the maximum and the time at whichthe other waveform reaches the minimum is reduced as the processingprogresses (as the remaining film thickness is reduced), that there is acorrelation between the time difference and the film thickness, and thatthe remaining film thickness (etching (trench) depth) and the end pointmay be determined by checking this time difference. The presentinvention is based on this fact.

[0056]FIG. 4 shows the operation flow of the semiconductor fabricatingapparatus shown in FIG. 1. In particular, the figure shows the flow ofoperation in which the etching state of a material to be processed isdetected for use in adjusting etching processing.

[0057] In this embodiment, the semiconductor fabricating apparatusreceives in step 800 the etching processing condition for thepoly-silicon film that is the material to be processed 40. In this step,the semiconductor fabricating apparatus may receive data from theprocessing condition database stored or recorded in a storage unit or arecording unit in advance or may receive data entered by the user via aninput device such as a keyboard or a mouse provided on the display 17.The semiconductor fabricating apparatus may also read film configurationdata from the cassette of the semiconductor wafer 4 or from the wafer 4itself and detect the data with an operation unit not shown.

[0058] Next, in step 801, the wavelength groups λ1 and λ2 fordetermining the etching state are detected by using data recorded on thedifferential data storage unit or by comparing the wavelengths with thedifferential data on intensities stored/recorded on a separatestorage/recording unit. In addition, the base time difference ΔT is setfor the time difference between the times corresponding to the opposedextreme values described above.

[0059] In steps 802, 803, and 804, the waveform data on the interferencelight obtained by processing the actual wafer 4 is detected, theinterference waveforms of determination wavelength groups λ1 and λ2 thatare set in step 801 are differentiated, and the times T1 and T2 at whichthe differential data becomes the extreme value in each wavelength groupare calculated.

[0060] In step 818, the comparator 16 is used as described above tocompare the time difference between T1 and T2 calculated in step 804(T1−T2 or T2−T1) with the base time difference ΔT that is set in step801. If T1−ΔT<T2<T1+ΔT is not satisfied, that is, if it is found thetime difference ΔT is smaller than the time difference between T1 andT2, the apparatus determines that the desired film thickness is notreached and passes control back to step 803 to continue processing onthe material to be processed 40. On the other hand, if T1−ΔT≦T2<T1+ΔT issatisfied, that is, if it is found that ΔT is equal to or larger thanthe time difference between T1 and T2, the apparatus determines that thedesired film thickness has been reached or exceeded and passes controlto step 814 to end etching and sampling.

[0061] In this embodiment, etching stops at this point. The sampling ofinterference lights belonging to the wavelength groups 1 and 2, which isperformed via the spectroscope 11, also stops.

[0062] The inventor and the colleagues have conducted a theoreticalinterference analysis of the material to be processed (poly-siliconfilm) 40 considering the effect of the undercoating material (oxidefilm) 42 to find that the interference waveform appearing when the filmthickness changes as a result of the etching of the material to beprocessed 40 depends on the thickness of the undercoating film (oxidefilm) 42.

[0063]FIGS. 5A-5D are diagrams showing the undercoating oxide filmdependence of the poly-silicon film thickness, where the differentialvalue of the measurement wavelength 400 nm and the measurementwavelength 380 nm zero-crosses from negative to positive when etchingprocessing is executed by the film thickness measuring apparatus shownin FIG. 1 and, with that film thickness, the undercoating oxide filmdependence of the wavelength where the differential value zero-crossesfrom positive to negative.

[0064] For a poly-silicon film about 60 nm thick, FIG. 5A shows thepoly-silicon film thickness with respect to the undercoating oxide filmthickness for a light with the wavelength of 400 nm that zero-crossesfrom negative to positive (minimum value is reached). As shown in thefigure, the poly-silicon film thickness changes cyclically at about 130nm increments in the undercoating oxide film thickness. This is becausethe undercoating oxide film interference occurs immediately after thepoly-silicon film interference.

[0065] That is, the poly-silicon film thickness changes cyclically everysin(4πnd/λ), where n is the refraction index of the undercoating oxidefilm, d is the thickness of the undercoating oxide film, and λ is thewavelength. FIG. 5B shows the wavelength group of waveforms thatzero-cross from positive to negative (maximum value is reached) when thelight with the wavelength of 400 nm zero-crosses from negative topositive for the poly-silicon film thickness. As shown in the figure,the wavelength group ranges from about 430 to 500 nm. Therefore, theapproximate thickness of the undercoating oxide film may be obtained bymeasuring the light with the wavelength of 400 nm and the wavelengthgroup of about 430 nm to 500 nm.

[0066] For example, when the extreme value of the wavelength of 400 nmmatches the extreme value of the wavelength of 440 nm, the thickness ofthe undercoating oxide film is several nm to 130 nm, about 170 nm to 260nm, or about 330 nm to 380 nm.

[0067] When the zero-cross of the wavelength of 400 nm, the wavelengthof 440 nm, and 480 nm match, the undercoating oxide film thickness isfound to be about 140 nm to 170 nm and about 300 nm to 330 nm. With thewafer product specifications taken into consideration, the undercoatingoxide film thickness is further limited. When the measurement wavelengthof 380 nm shown in FIG. 5C zero-crosses from negative to positive usingthe undercoating oxide film thickness (about 300 nm to 320 nm) obtainedas described above, the wavelength group λ2 that zero-crosses frompositive to negative is narrowed to about 410 nm to 420 nm (about 410 nmto 450 nm) (see FIG. 5D). At the same time, the accuracy of thepoly-silicon film thickness is increased from about 48 nm-56 nm to about52 nm-55 nm.

[0068] A plurality of spectroscopes may be used to measure and control awide range of the area of a member to be processed.

[0069] Without using a light source that supplies a light to the vacuumchamber 2 as in the above embodiment, an interference light may also bemeasured by a measuring instrument via the spectroscope 11 using a lightfrom the plasma 3 generated in the vacuum chamber 2. In this case, theplasma light reflected on the surface of the wafer 4 is supplied to thespectroscope 11. In addition, to measure a change in the plasma light, ameasurement port and an optical transmission unit are provided on theside wall of the vacuum chamber 2 such that the light inside the chambermay be received. The signal detected by them is used as a referencelight. This reference light must be a light that does not pass throughthe light path into which the light from the wafer surface directlyenters and that can detect a change in the plasma light. In thisembodiment, the plasma light is received by the light receiver providedon the side wall.

[0070] Next, a second embodiment of the present invention will bedescribed with reference to FIGS. 6, 7A, 7B, and 8.

[0071]FIGS. 6, 7A, and 7B are diagrams showing interference waveformsdetected by a semiconductor fabricating apparatus in the secondembodiment of the present invention.

[0072] The left-hand side graph in FIG. 6 shows a change in theinterference light intensity with the wavelength on the vertical axisand the film thickness (processing time) on the horizontal axis. Theright-hand side graph shows a change in the intensity in the wavelengtharea ranging from 300 nm or shorter to 700 nm or longer at a specifictime indicated by the dotted line in the left-hand side graph.

[0073] This figure shows that the interference light greatly changesaround a specific wavelength and that the differential data on theintensity fluctuates widely. As with FIG. 6, FIGS. 7A and 7B show achange in the interference light intensity with the wavelength on thevertical axis and the film thickness (processing time) on the horizontalaxis. FIG. 7A shows the change when the thickness of an oxide film 42formed below the poly-silicon film that is a material to be processed 40is 290 nm, while FIG. 7B shows the change when the thickness of theundercoating oxide film is 330 nm. The inventor and the colleagues havefound that, as shown in the figures, the wavelength value at which theintensity of the interference light differential data fluctuates widelydepends on the thickness of the undercoating oxide film 42, that is,there is a correlation between the wavelength and the thickness of theundercoating oxide film 42 and, therefore, the thickness of theundercoating oxide film may be detected using interference light dataobtained when the film, which is above the oxide film and which is to beprocessed, is etched. This embodiment of the present invention is basedon this fact.

[0074]FIG. 8 is a flowchart showing the flow of the operation of asemiconductor fabricating apparatus in the embodiment based on theinterference waveforms shown in FIGS. 6, 7A, and 7B. In this embodiment,the intensity of an interference light with the wavelength ranging fromabout 300 nm to 700 nm is obtained during poly-silicon gate etching andits differential data is calculated. Instead of a zero-crossing (extremevalue is reached) wavelength is shifted sequentially to the short waveside as the film thickness of the polysilicon film to be processed 40 isdecreased, the wavelength in the short wave side is reversed before thewavelength in the long wave side because of the undercoating oxide filmthickness. This characteristic is used to calculate the undercoatingoxide film thickness from the reversed wavelength.

[0075] This enables the thickness of the undercoating film (undercoatingoxide film), which has been determined by measuring a sample wafer, tobe detected using the interference light data obtained when the filmabove the undercoating film is processed. This minimizes a throughputdecrease or a fabrication cost increase that has been caused by themeasurement of a sample.

[0076] Using the undercoating oxide film thickness calculated asdescribed above can also increase the accuracy in the thicknessmeasurement of a poly-silicon film that is the material to be processed.

[0077] In FIG. 8, the etching condition (etching discharge condition,etching remaining film thickness condition) for the material to beprocessed (polysilicon film) is entered (step 900). Based on the etchingremaining film thickness condition, the two determination wavelengthgroups λ1 and λ2, their zero-cross directions, and the determinationtime width AT are set from data stored in the data storage unit (step901).

[0078] Next, the etching and sampling of the wafer 4 is started (step902), the differential coefficient time series data Di,j is calculatedfrom the multiple-wavelength output signal yi,j received from thespectroscope (step 903), and the wavelength λi at which the zero-crosstimes Ti and Tm of the differential coefficient time series data Di,jand Dm,j are reversed is calculated (904), where i is the measuredwavelength in the long wavelength side and m is the measured wavelengthin the short wavelength side.

[0079] The times Ti and Tm satisfy the relation Ti<Tm in the wavelengtharea where there is no effect of the undercoating oxide film, while thetimes Ti and Tm satisfy the relation Ti>Tm in the wavelength area wherethere is the effect of the undercoating oxide film. From theundercoating oxide film thickness and the distortion wavelength valuewhich have this wave-length λi in the database in advance, theundercoating oxide film thickness is calculated (step 905). Then, usingthe calculated undercoating oxide film thickness, the two determinationwavelength groups λ1 and λ2 are reset from the differential zero-crosstable (step 906).

[0080] The interference waveform of the two determination wavelengthgroups λ1 and λ2 that have been reset is differentiated (step 907).Next, the time difference ΔT that is the base value set in step 901 iscompared with the time difference between the zero-cross times T1 andT2, that is, a check is made if the relation T1−ΔT≦T2≦T1+ΔT is satisfied(step 908) to determine if etching and sampling should be ended (step909). If the comparison between the time difference ΔT and the timedifference between the zero-cross times T1 and T2 (check if the relationT1−ΔT≦T2≦T1+ΔT is satisfied: step 908) results in “NO”, the operation isrepeated beginning in step 903. If the undercoating oxide film thicknessis calculated, steps 903 to 905 need not necessarily be executed. On theother hand, if the comparison results in “YES” in step 908, control ispassed to step 909 to end etching and sampling.

[0081] In contrast to the prior art in which the processing throughputand the cost are high because a sample wafer must be measured, theapparatus according to the present invention allows data, obtainedduring the processing of an upper-layer film, to be used to detect thefilm thickness of a lower-layer film, thus increasing the processingthroughput of the whole apparatus and reducing the cost.

[0082] It should be further understood by those skilled in the art thatalthough the foregoing description has been made on embodiments of theinvention, the invention is not limited thereto and various changes andmodifications may be made without departing from the spirit of theinvention and the scope of the appended claims.

What is claimed is:
 1. A semiconductor fabricating apparatus etching asemiconductor wafer, placed in a chamber and having films thereon, usingplasma generated in the chamber, said semiconductor fabricatingapparatus comprising: a detector that detects a change in an amount oflight with at least two wavelengths obtained from a surface of the waferfor a predetermined time during the processing; and a determination unitthat compares an interval between a time at which an amount of lightwith one of the two wavelengths is maximized and a time at which anamount of light with the other wavelength is minimized with apredetermined value to determine a state of the etching.
 2. Thesemiconductor fabricating apparatus according to claim 1, wherein saiddetermination unit determines a thickness of the film being etched ifthe interval is determined to be smaller than the predetermined value.3. The semiconductor fabricating apparatus according to claim 1, whereinsaid determination unit stops the etching processing if the interval isdetermined to be smaller than the predetermined value.
 4. Asemiconductor fabricating apparatus comprising: a detector that, when asemiconductor wafer placed in a chamber is etched using plasma generatedin the chamber, detects a light interference from a surface of the waferfor a predetermined time during the etching processing; and a controlunit that compares an interval between a time at which an amount oflight with one of at least two wavelengths output from said detector ismaximized and a time at which an amount of light with the otherwavelength is minimized with a predetermined value to control theetching processing.
 5. The semiconductor fabricating apparatus accordingto claim 4, wherein said control unit stops the etching processing ifthe interval is determined to be smaller than the predetermined value.6. A semiconductor fabricating apparatus etching a semiconductor wafer,placed in a chamber and having a multiple-layer film composed of a firstfilm formed a surface thereof and a second film formed on the firstfilm, using plasma generated in the chamber, said semiconductorfabricating apparatus comprising: a light detector that detects a changein an amount of light with a plurality of wavelengths obtained from asurface of the wafer for a predetermined time during which the secondfilm is etched; and a detection unit that detects a thickness of thefirst film based on a specific waveform obtained from an output of saiddetector.
 7. The semiconductor fabricating apparatus according to claim6, wherein, when said light detector detects, for the plurality ofwavelengths, a change in an amount of interference light from thesurface of the wafer with respect to time, said detection unit detects acharacteristic change in an output of said light detector.
 8. Asemiconductor fabricating apparatus etching a semiconductor wafer,placed in a chamber and having a multiple-layer film composed of anoxide film formed a surface thereof and a film formed on the oxide film,using plasma generated in the chamber, said semiconductor fabricatingapparatus comprising: a light detector that detects an amount of lightwith a plurality of wavelengths obtained from a surface of the wafer fora predetermined time during which the film formed on the oxide film isetched; and a detection unit that detects a thickness of the oxide filmbased on a specific waveform obtained from an output of said detector.9. The semiconductor fabricating apparatus according to claim 8,wherein, when said light detector detects, for the plurality ofwavelengths, a change in an amount of interference light from thesurface of the wafer with respect to time, said detection unit detects acharacteristic change in an output of said light detector.